Unknown Dendrobium nobile black spots and streaks

[carnegieo575]

Hello everyone,

I have a Dendrobium Nobile that I got back in March of this year. I need help identifying what exactly these ailments are since I can't seem to find info specific to dendros.

I noticed when I got it, it had what looked like this kind of black powdery mildew on the leaf sheaths that attach to the canes. Then, about once a month I've noticed a dark spot or two show up on various leaves. If I leave it, it expands a bit and starts to turn the leaf yellow. I've removed those as I've seen them, but now that it's getting to the new growth and as you can see in the pics, the spots are like, in the crease of the leaves and it seems different than the other black circular spots and is deforming new leaves. I assume this is bacterial or fungal, but don't know. My culture has been good and I assume this is stemming from the mildewy spots from when I got it from the greenhouse that are now spreading.

I soaked the entire plant in Physan 20 when I repotted it a month or two ago as a precaution, have sprayed a few times with peroxide, and cinnamon doesn't help at all. It seems completely healthy otherwise. It does get plenty of light, moderate temps and good air movement. So we can rule out cool, damp, stagnant conditions. I sprayed peroxide just before taking the pics that's why the leaves are a bit wet.

I was gonna jump the gun on some Phyton 27 to see if something systematic works, but now I'm reading that you shouldn't use copper based treatments on Dendrobiums. But... no one seems to actually back up their statement with factual information as to why. Anyone have any insight, if I should use Phyton, if there's another option for systematics for use on Dendrobiums, thoughts? Thanks I really want to save this one.

[rbarata]

Nothing to worry about...what's your humidity level?

[carnegieo575]

Really...?
Humidity varies throughout the year here in WI tremendously. I struggle to keep above 40% indoors during the winter months. Starts to climb gradually indoors between 50 and 70% through the summer and have been keeping it outdoors since it's gotten warmer. So in general I'd say between 30 and 80% throughout the year give or take.

[rbarata]

I said it's ok because my nobile has spots like that...they lose leaves in the older pbulbs (sometimes with 1 year only) and the sheaths covering them also get dry and gain some bad looking.
But maybe the spots are caused by high humidity, with heat it's prone to grow fungus and stuff like that.
Reduce the humidity, increase air flow but keep it well watered during warmer weather. In winter they need to be somewhat dry (rest).

[carnegieo575]

I gotcha. Alright, well let's see what happens throughout the summer then! Glad to hear it's pretty common. Dendrobium is not a common genus to see being sold around here. I was honestly worried this was something that was going to spread quickly and kill the plant if left unchecked. Thanks for taking a look